Method and apparatus for processing a medium dynamic range video signal in SL-HDR2 format

ABSTRACT

A medium dynamic range video signal and associated metadata are received, wherein the metadata include data representative of a peak luminance value of the signal. The medium dynamic range video signal is processed in a first mode to reconstruct a high dynamic range video signal based on a received standard dynamic range video signal and associated metadata if the peak luminance value of the medium dynamic range video signal is smaller than the peak luminance value of a presentation display, and in a second mode to optimize a received high dynamic range video signal for a rendering device if the peak luminance value of the medium dynamic range video signal is greater than the peak luminance value of the presentation display.

This application claims the benefit, under 35 U.S.C. § 365 ofInternational Application PCT/US2019/041275, filed Jul. 11, 2019, whichwas published in accordance with PCT Article 21(2) on Jan. 23, 2020, inEnglish, and which claims the benefit of European Patent Application No.18305993.0, filed Jul. 20, 2018.

FIELD

The present principles relate to distributing HDR video signals ofmedium peak luminance.

BACKGROUND

The present section is intended to introduce the reader to variousaspects of art, which may be related to various aspects of the presentprinciples that are described and/or claimed below. This discussion isbelieved to be helpful in providing the reader with backgroundinformation to facilitate a better understanding of the various aspectsof the present principles. Accordingly, it should be understood thatthese statements are to be read in this light, and not as admissions ofprior art.

In the following, image data refer to one or several arrays of samples(pixel values) in a specific image/video format which specifies allinformation relative to the pixel values of an image (or a video) andall information which may be used by a display and/or any otherapparatus to visualize and/or decode an image (or video) for example. Animage comprises a first component, in the shape of a first array ofsamples, usually representative of luminance (or luma) of the image, anda second and third component, in the shape of other arrays of samples,usually representative of the chrominance (or chroma) of the image. Or,equivalently, the same information may also be represented by a set ofarrays of color samples, such as the traditional tri-chromatic RGBrepresentation.

A pixel value is represented by a vector of C values, where C is thenumber of components. Each value of a vector is represented with anumber of bits which defines a dynamic range of the pixel values.

Standard Dynamic Range images (SDR images) are images whose luminancevalues are represented with a limited number of bits (typically 8). Thislimited representation does not allow correct rendering of small signalvariations, in particular in dark and bright luminance ranges. In HighDynamic Range images (HDR images), the signal representation is extendedto maintain a high accuracy of the signal over its entire range. In HDRimages, pixel values are usually represented in floating-point format(typically at least 10 bits per component, namely float or half-float),the most popular format being openEXR half-float format (16-bit per RGBcomponent, i.e. 48 bits per pixel) or in integers with a longrepresentation, typically at least 16 bits.

The advent of the High Efficiency Video Coding (HEVC) standard (ITU-TH.265 Telecommunication standardization sector of ITU (02/2018), seriesH: audiovisual and multimedia systems, infrastructure of audiovisualservices—coding of moving video, High efficiency video coding,Recommendation ITU-T H.265) enables the deployment of new video serviceswith enhanced viewing experience, such as Ultra HD services. In additionto an increased spatial resolution, the Ultra HD format can bring awider color gamut (WCG) and a higher dynamic range (HDR) than theStandard Color Gamut (SCG) and the Standard Dynamic Range (SDR),respectively, of the High Definition format currently deployed.Different solutions for the representation and coding of HDR/WCG videohave been proposed such as the perceptual transfer function basedPerceptual Quantizer (PQ) (SMPTE ST 2084, “High Dynamic RangeElectro-Optical Transfer Function of Mastering Reference Displays”,Society of Motion Picture and Television Engineers, 2014, or Diaz, R.,Blinstein, S. and Qu, S. “Integrating HEVC Video Compression with a HighDynamic Range Video Pipeline”, SMPTE Motion Imaging Journal, Vol. 125,Issue 1. February, 2016, pp 14-21). Typically, SMPTE ST 2084 allows torepresent HDR video signal of up to 10 000 cd/m² peak luminance withonly 10 or 12 bits.

SDR backward compatibility with decoding and rendering apparatus is animportant feature in some video distribution systems, such asbroadcasting or multicasting systems. A solution based on a single layercoding/decoding process may be backward compatible, e.g. SDR compatible,and may leverage legacy distribution networks and services already inplace.

Such a single layer based distribution solution enables both highquality HDR rendering on HDR-enabled Consumer Electronic (CE) devices,while also offering high quality SDR rendering on SDR-enabled CEdevices. Such a solution is based on an encoded signal, e.g. SDR signal,and associated metadata (few bytes per video frame or scene) that can beused to reconstruct another signal, e.g. either SDR or HDR signal, froma decoded signal.

An example of a single layer based distribution solution may be found inthe ETSI technical specification TS 103 433-1 V1.2.1 (August 2017). Sucha single layer based distribution solution is denoted SL-HDR1 in thefollowing.

Additionally, HDR distribution systems (workflows but also decoding andrendering apparatus) may be already deployed. Indeed, there are a numberof global video services providers which include HDR content. However,distributed HDR material may be represented in a format or withcharacteristics which do not match consumer end-device characteristics.Usually, the consumer end-device adapts the decoded material to its owncharacteristics. However, the versatility of technologies employed inthe HDR TV begets important differences in terms of rendition because ofthe differences between the consumer end-device characteristics comparedto the mastering display used in the production environment to grade theoriginal content. For content producer, artistic intent fidelity and itsrendition to the consumer are of utmost importance. Thus, “displayadaptation” metadata generated either at the production stage duringgrading process or under the control of a quality check operator beforeemission enable the conveyance of the artistic intent to the consumerwhen the decoded signal is to be adapted to end-device characteristics.

An example of a single layer based distribution solution combined withdisplay adaptation may be found in ETSI technical specification TS 103433-2 V1.1.1 (January 2018). Such a single layer based distributionsolution is denoted SL-HDR2 in the following.

Such single layer based distribution solution, SL-HDR1 or SL-HDR2,generates metadata as parameters used for the reconstruction of thesignal. Metadata may be either static or dynamic.

Static metadata means parameters representative of the video content orits format that remain the same for a video (set of images) and/or aprogram.

Static metadata are valid for the whole video content (scene, movie,clip . . . ) and may depend on the image content per se or therepresentation format of the image content. They may define, forexample, the image format or color space or color gamut, respectively.For instance, SMPTE ST 2086:2014, “Mastering Display Color VolumeMetadata Supporting High Luminance and Wide Color Gamut Images” definesuch a kind of static metadata which describe the mastering display usedto grade the material in a production environment. The Mastering DisplayColour Volume (MDCV) SEI (Supplemental Enhanced Information) message isused for the distribution of ST 2086 for both H.264/AVC (“Advanced videocoding for generic audiovisual Services”, SERIES H: AUDIOVISUAL ANDMULTIMEDIA SYSTEMS, Recommendation ITU-T H.264, TelecommunicationStandardization Sector of ITU, April 2017) and HEVC video codecs.

Dynamic metadata is content-dependent information, so that metadatacould change with the image/video content, e.g. for each image or foreach group of images. As an example, SMPTE ST 2094:2016 standardsfamilies, “Dynamic Metadata for Color Volume Transform” are dynamicmetadata typically generated in a production environment. SMPTE ST2094-30 can be distributed along HEVC and AVC coded video stream thanksto the Colour Remapping Information (CRI) SEI message.

There are pay TV operators interested in Medium Dynamic Rangebroadcasting. Basically, it consists in transmitting an HDR video ofmedium peak luminance. Consumer displays with higher peak luminance,up-map the signal while those with lower peak luminance down-map thesignal. SL-HDR2 can operate MDR distribution however the currentup-mapping feature rests upon extrapolation while the distributed MDRsignal comes from a down-mapped original HDR signal (with higher peakluminance).

The present embodiments have been devised with the foregoing in mind.

SUMMARY

The following presents a simplified summary of the present principles inorder to provide a basic understanding of some aspects of the presentprinciples. This summary is not an extensive overview of the presentprinciples. It is not intended to identify key or critical elements ofthe present principles. The following summary merely presents someaspects of the present principles in a simplified form as a prelude tothe more detailed description provided below.

According to an aspect of the present disclosure, a method forprocessing a video signal is disclosed. Such a method comprises:

-   -   receiving a medium dynamic range video signal and associated        metadata, said metadata including data representative of a peak        luminance value of the medium dynamic range video signal;    -   receiving data representative of a peak luminance value of a        presentation display;    -   determining whether the peak luminance value of the medium        dynamic range video signal is greater or lower than the peak        luminance value of the presentation display;    -   configuring a processor based on the determination, wherein the        processor has a first mode to reconstruct a high dynamic range        video signal based on a received standard dynamic range video        signal and associated metadata, and a second mode to optimize a        received high dynamic range video signal for the rendering        device; and    -   processing the medium dynamic range video signal by the        processor in the first mode if the peak luminance value of the        medium dynamic range video signal is smaller than the peak        luminance value of the presentation display and in the second        mode if the peak luminance value of the medium dynamic range        video signal is greater than the peak luminance value of the        presentation display.

According to another aspect of the present disclosure, a processor forprocessing a video signal is disclosed, wherein the processor has afirst mode to reconstruct a high dynamic range video signal based on areceived standard dynamic range video signal and associated metadata,and a second mode to optimize a received high dynamic range video signalfor the rendering device. Such a processor comprises:

-   -   means for receiving a medium dynamic range video signal and        associated metadata, said metadata including data representative        of a peak luminance value of the medium dynamic range video        signal;    -   means for receiving data representative of a peak luminance        value of a presentation display;    -   means for determining whether the peak luminance value of the        medium dynamic range video signal is greater or lower than the        peak luminance value of the presentation display; and    -   means for processing the medium dynamic range video signal in        the first mode if the peak luminance value of the medium dynamic        range video signal is smaller than the peak luminance value of        the presentation display and in the second mode if the peak        luminance value of the medium dynamic range video signal is        greater than the peak luminance value of the presentation        display.

The present disclosure also provides an apparatus comprising a processoraccording to the preceding description. The present embodiments alsoprovide a computer program product including instructions, which, whenexecuted by a computer, cause the computer to carry out the methodsdescribed.

The specific nature of the present principles as well as other objects,advantages, features and uses of the present principles will becomeevident from the following description of examples taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings, examples of the present principles are illustrated.

FIG. 1 shows a high-level representation of an end-to-end workflowsupporting content delivery to displays with improved display adaptationfeature in accordance with an example of the present principles;

FIG. 2 shows an end-to-end workflow supporting content production anddelivery to HDR and SDR CE displays in accordance with a single layerbased distribution solution;

FIG. 3 shows a particular implementation of the workflow of FIG. 2;

FIG. 4a shows an illustration of a perceptual transfer function;

FIG. 4b shows an example of a piece-wise curve used for mapping;

FIG. 4c shows an example of a curve used for converting back aperceptual uniform signal to a linear-light domain;

FIG. 5 shows an exemplary embodiment of an architecture of a apparatuswhich may be configured to implement a method described in relation withFIG. 1 to FIG. 4 c;

FIG. 6 shows schematically an MDR distribution use case;

FIG. 7 shows schematically a S-LHDR-2 built-in display mapping;

FIG. 8 shows schematically a S-LHDR-2 solution for addressing MDR;

FIG. 9 shows schematically an example of the present embodiments foraddressing MDR; and

FIG. 10 shows a diagram of the adapted SL-HDR post-processor logic;

Similar or same elements are referenced with the same reference numbers.

DESCRIPTION OF EXAMPLE OF THE PRESENT PRINCIPLES

The present principles will be described more fully hereinafter withreference to the accompanying figures, in which examples of the presentprinciples are shown. The present principles may, however, be embodiedin many alternate forms and should not be construed as limited to theexamples set forth herein. Accordingly, while the present principles aresusceptible to various modifications and alternative forms, specificexamples thereof are shown by way of examples in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the present principles to the particularforms disclosed, but on the contrary, the disclosure is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the present principles as defined by the claims.

The terminology used herein is for the purpose of describing particularexamples only and is not intended to be limiting of the presentprinciples. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising,” “includes” and/or “including” when used inthis specification, specify the presence of stated features, integers,steps, operations, elements, and/or components but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof. Moreover, whenan element is referred to as being “responsive” or “connected” toanother element, it can be directly responsive or connected to the otherelement, or intervening elements may be present. In contrast, when anelement is referred to as being “directly responsive” or “directlyconnected” to other element, there are no intervening elements present.As used herein the term “and/or” includes any and all combinations ofone or more of the associated listed items and may be abbreviated as“/”.It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement without departing from the teachings of the present principles.Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows. Some examples are described with regard to block diagrams andoperational flowcharts in which each block represents a circuit element,module, or portion of code which comprises one or more executableinstructions for implementing the specified logical function(s). Itshould also be noted that in other implementations, the function(s)noted in the blocks may occur out of the order noted. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently or the blocks may sometimes be executed in the reverseorder, depending on the functionality involved. Reference herein to “inaccordance with an example” or “in an example” means that a particularfeature, structure, or characteristic described in connection with theexample can be included in at least one implementation of the presentprinciples. The appearances of the expression “in accordance with anexample” or “in an example” in various places in the specification arenot necessarily all referring to the same example, nor are separate oralternative examples necessarily mutually exclusive of other examples.Reference numerals appearing in the claims are by way of illustrationonly and shall have no limiting effect on the scope of the claims. Whilenot explicitly described, the present examples and variants may beemployed in any combination or sub-combination.

Typically, two different images have different dynamic range of theluminance. The dynamic range of the luminance of an image is the ratiobetween the maximum over the minimum of the luminance values of saidimage.

Typically, when the dynamic range of the luminance of an image is below1000 (e.g. 500:100 cd/m² over 0.2 cd/m²), said image is denoted as aStandard Dynamic Range (SDR) image and when the dynamic range of theluminance of an image is equal or greater than 1000 (e.g. 10000:1000cd/m² over 0.1 cd/m²), said image is denoted as an HDR image. Luminanceis expressed by the unit candela per square meter (cd/m²). This unitsupersedes the term “nit” which may also be used (although it isdeprecated in the International System of Units).

The present principles are described for pre-processing, encoding,decoding and post-processing an image but extends to pre-processing,encoding, decoding and post-processing of a sequence of images (video)because each image of the sequence is sequentially pre-processed,encoded, decoded and post-processed as described below.

FIG. 1 shows a high-level representation of an end-to-end workflowsupporting content delivery to displays with improved display adaptationfeature in accordance with an example of the present principles. Theapparatus A1 is configured to implement a method for pre-processing andencoding an image or a video stream, the apparatus A2 is configured toimplement a method for decoding and post-processing an image or videostream as described below, and the apparatus A3 is configured to displaythe decoded and post-processed image or video stream. The two remoteapparatuses A1 and A2 are communicating over a distribution network NETthat is configured at least to provide the encoded image or video streamfrom apparatus A1 to apparatus A2.

Apparatus A1 comprises at least one device configured to implement apre-processing and/or encoding method as described herebelow. Said atleast one device belongs to a set of devices comprising a mobile device,a communication device, a game device, a tablet (or tablet computer), acomputer device such as a laptop, a still image camera, a video camera,an encoding chip, a still image server and a video server (e.g. abroadcast server, a video-on-demand server or a web server).

Apparatus A2 comprises at least one device configured to implement adecoding and/or post-processing method as described herebelow. Said atleast one device belongs to a set of devices comprising a mobile device,a communication device, a game device, a computer device and a set topbox.

Apparatus A3 comprises at least one device configured to implement adisplaying method. Said at least one device belongs to a set of devicescomprising a TV set (or television), a tablet (or tablet computer), acomputer device such as a laptop, a display, a head-mounted display anda rendering/displaying chip.

In accordance with an example, the network is a broadcast network,adapted to broadcast still images or video images from apparatus A1 to aplurality of apparatuses A2. DVB and ATSC based networks are examples ofsuch broadcast networks.

In accordance with another example, the network is a broadband networkadapted to deliver still images or video images from apparatus A1 to aplurality of apparatuses A2.

Internet-based networks, GSM networks or TV over IP networks areexamples of such broadband networks.

In an exemplary embodiment, the end-to-end workflow uses a broadcastserver for apparatus A1, a set top box for apparatus A2, a televisionset for apparatus A3 and a DVB terrestrial broadcast network.

In an alternate embodiment, apparatus A2 and A3 are combined in a singledevice, for example a television integrating set top box decoding andpost-processing functionalities.

In an alternate embodiment, the distribution network NET is replaced bya physical packaged media on which the encoded image or video stream isstored.

Physical packaged media comprise optical packaged media such a Blu-raydisc and Ultra HD Blu-ray but also memory-based package media such asused in OTT and VoD services.

FIG. 2 shows an end-to-end workflow supporting content production anddelivery to HDR and SDR CE displays in accordance with a single layerbased distribution solution.

Basically, said single layer based distribution solution may address SDRdirect backward compatibility i.e. it leverages SDR distributionnetworks and services already in place and enables high quality HDRrendering on HDR-enabled CE devices including high quality SDR renderingon SDR CE devices.

SL-HDR1 is one example of such single layer based distribution solution.

But, said single based layer distribution solution may also relate to asolution used on distribution networks for which display adaptationdynamic metadata are delivered along with an PQ HDR video signal. PQmeans “Perceptual Quantization” as defined in Recommendation ITU-RBT.2100-1, “Image parameter values for high dynamic range television foruse in production and international programme exchange”.

The workflow shown in FIG. 2 involves a single layer-based distributionsolution with associated metadata and illustrates an example of the useof a method for reconstructing three components {C₃₀ ^(m)}representative of three components {C₁₀ ^(m)} of an input image fromthree decoded components {

} representative of a decoded image and said metadata as specified, forexample, in SL-HDR1 or SL-HDR2.

An information data ID determines which single layer based distributionsolution has to be considered. Usually, in practice only one singlebased layer distribution solution is instantiated and the informationdata ID is a fixed value. If more than one single layer baseddistribution solutions are instantiated, then the information data IDindicates which of these single layer based distribution solutions hasto be considered.

Typically, SL-HDR1 and SL-HDR2 may be instantiated and the informationdata ID indicates if either SL-HDR1 or SL-HDR2 has to be considered.

Basically, the single layer based distribution solution shown in FIG. 2comprises a pre-processing step 20, an encoding step 23, decoding steps25 and 26 and a post-processing step 28.

In the following, a component C_(n) ^(m) designates a component m of animage n. These components C_(n) ^(m) represent an image I_(n) in aspecific image format. Typically, an image format is characterized by acolor volume (e.g. chromaticity and dynamic range), a color encodingsystem (e.g. RGB, YCbCr).

The input and the output of the pre-processing step 20 are imagesrepresented by three components denoted {C₁ ^(m)} and {C₁₂ ^(m)}respectively, and the input and the output of the post-processing step28 are images represented by three components denoted {C₂ ^(m)} and {C₃^(m)} respectively.

The single layer based distribution solution shown in FIG. 2 maycomprise format adaptations steps 21, 22, 27, 29 to adapt the format ofthree components {C_(n) ^(m)} to the input of a further processing to beapplied on these components.

For example, in step 21 (optional), the format of the three components{C₁₀ ^(m)} are adapted to a format fitting an input format of thepre-processing step 20.

For example, the component C₁ ¹ is a non-linear signal, denoted luma inliterature, which is obtained from the gamma-compressed components {C₁₀^(m)} by:

$C_{1}^{1} = {A_{1}\begin{bmatrix}{C_{10}^{1}}^{1/\gamma} \\{C_{10}^{2}}^{1/\gamma} \\{C_{10}^{3}}^{1/\gamma}\end{bmatrix}}$

and the component q, C₁ ², C₁ ³ are obtained by applying a gammacompression to the components of the input image:

$\begin{bmatrix}C_{1}^{2} \\C_{1}^{3}\end{bmatrix} = {\begin{bmatrix}A_{2} \\A_{3}\end{bmatrix}\mspace{11mu}\begin{bmatrix}{C_{10}^{1}}^{1/\gamma} \\{C_{10}^{2}}^{1/\gamma} \\{C_{10}^{3}}^{1/\gamma}\end{bmatrix}}$

where γ is a gamma factor, preferably equal to 2.4, A=[A₁ A₂ A₃]^(T) isa conversion matrix comprising three 1×3 sub-matrices A₁, A₂, A₃ whereA ₁=[A ₁₁ A ₁₂ A ₁₃]A ₂=[A ₂₁ A ₂₂ A ₂₃]A ₃=[A ₃₁ A ₃₂ A ₃₃]

with A_(mn) (m=1, . . . , 3, n=1, . . . 3) are sub-matrix coefficients.

For example, the conversion matrix A may be the canonical 3×3R′G′B′-to-Y′CbCr conversion matrix as specified in Recommendation ITU-RBT.2020-2 or Recommendation ITU-R BT.709-6 when the three components{C₁₀ ^(m)} are RGB components.

When BT.2020 color gamut is considered,

$A = {\begin{bmatrix}A_{1} \\A_{2} \\A_{3}\end{bmatrix} = \begin{bmatrix}{{0.2}627} & {{0.6}78} & {{0.0}593} \\{{- {0.1}}3963} & {{- {0.3}}6037} & {0.5} \\{0.5} & {{- {0.4}}59786} & {{- {0.0}}40214}\end{bmatrix}}$

When BT.709 color gamut is considered,

$A = {\begin{bmatrix}A_{1} \\A_{2} \\A_{3}\end{bmatrix} = \begin{bmatrix}{{0.2}126} & {{0.7}152} & {{0.0}722} \\{{- {0.1}}14572} & {{- {0.3}}85428} & {0.5} \\{0.5} & {{- {0.4}}54153} & {{- {0.0}}45847}\end{bmatrix}}$

The convertion matrix A is invertible. For example, the inverse of thematrix A, denoted A⁻¹, is given by

$A^{- 1} = \begin{bmatrix}1 & 0 & A_{13}^{\prime} \\1 & A_{22}^{\prime} & A_{23}^{\prime} \\1 & A_{32}^{\prime} & 0\end{bmatrix}$

with A′_(mn) (m=1, . . . , 3, n=1, . . . 3) are sub-matrix coefficients.

When BT.2020 color gamut is considered,

$A^{- 1} = \begin{bmatrix}1 & 0 & {{1.4}746} \\1 & {{- {0.1}}6455} & {{- {0.5}}7135} \\1 & {{1.8}814} & 0\end{bmatrix}$

and when BT.709 color gamut is considered,

$A^{- 1} = \begin{bmatrix}1 & 0 & {{1.5}748} \\1 & {{- {0.1}}8733} & {{- {0.4}}6813} \\1 & {{1.8}5563} & 0\end{bmatrix}$

Said input format adaptation step 21 may also include adapting the bitdepth of the input image I₁ to bit depth such as 10 bits for example, byapplying a transfer function on at least one of the three components{C₁₀ ^(m)} of an input image such as a PQ or HLG transfer function orits inverse (Rec. ITU-R BT.2100).

In step 22 (optional), the format of the three components {C₁₂ ^(m)} mayalso be adapted to a format fitting the input format of the encodingstep 23.

In step 27, (optional) the format of the three components {

} may be adapted to a format fitting the input of the post-processingstep 28, and in step 29, the format of the three components {C₃ ^(m)}may be adapted to a format that may be defined from at least onecharacteristic of a targeted apparatus (e.g. a Set-Top-Box, a connectedTV, HDR/SDR enabled CE device, an Ultra HD Blu-ray disc player). In step21, the inverse of the matrix A is used.

Said format adaptation steps (21, 22, 27, 29) may include other colorspace conversion and/or color gamut mapping (and/or inverse color gamutmapping). Inverse gamut mapping may be used, for example, when the threedecoded components {

} and the three components {C₃₀ ^(m)} of an output image or the threecomponents {C₁₀ ^(m)} of an input image are represented in differentcolor spaces and/or gamut.

Usual format adapting processes may be used such as R′G′B′-to-Y′CbCr orY′CbCr-to-R′G′B′ conversions, BT.709-to-BT.2020 or BT.2020-to-BT.709,down-sampling or up-sampling chroma components, etc.

For example, SL-HDR1 may use format adapting processes and inverse gamutmapping as specified in Annex D of the ETSI technical specification TS103 433-1 V1.2.1 (August 2017).

In the pre-processing step 20, the three components {C₁ ^(m)} aredecomposed into three components {C₁₂ ^(m)} (which format may have beenpossibly adapted during step 22 to get the three components {C₁₂₀ ^(m)})and a set of parameters SP, and a switching step 24 determines if thethree components {C₂₀ ^(m)} are either the three components {C₁ ^(m)} orthe three components {C₁₂ ^(m)} or {C₁₂₀ ^(m)}) which are encoded in thebitstream B (step 23).

In step 23, the three components {C₂₀ ^(m)} may be encoded with anyvideo codec and a signal comprising the bitstream B is carriedthroughout a distribution network.

According to variant step 23, the set of parameters SP and/or theinformation data ID are conveyed as associated static and/or dynamicmetadata in the bitstream B.

According to a variant, the set of parameters SP and/or the informationdata ID are conveyed as associated static and/or dynamic metadata on aspecific channel.

Then, at least one signal, intended to be decoded by the apparatus A2 ofFIG. 1, carries the bitstream B and the accompanying metadata.

In a variant, the bitstream B is stored on a storage medium such as aBlu-ray disk or a hard disk or a memory of a Set-Top-Box for example.

In a variant, at least some accompanying associated metadata is storedon a storage medium such as an UltraHD Blu-ray disk or a hard disk or amemory of a Set-Top-Box for example.

Preferably, in step 23, a sequence of at least one triplet of components{C₂₀ ^(m)}, each representing an image, and possibly associated metadataare encoded with a video codec such as the H.265/HEVC codec orH.264/AVC.

In step 25, the set of parameters SP is obtained at least partiallyeither from the bitstream B or from another specific channel. At leastone of the parameters of the set of parameters SP may also be obtainedfrom a separate storage medium.

In step 26, the three decoded components {

} are obtained from the bitstream B.

In the post-processing step 28, which is a nearby functional inverse ofthe pre-processing step 20, the three components {C₃₀ ^(m)} arereconstructed from the three decoded components {

} and the obtained set of parameters SP.

In more detail, the pre-processing step 20 comprises steps 200-203.

In step 200, a component C_(1,pre) ¹ is obtained by applying a mappingfunction on the component C₁ ¹ which represents the luminance of theinput image.

Mathematically speaking,C _(1,pre) ¹ =MF(C ₁ ¹)with MF being a mapping function that may reduce the dynamic range ofthe luminance of an image. Note that its inverse, denoted IMF, mayinversely increase the dynamic range of the luminance of an image.

In step 202, a reconstructed component

is obtained by applying an inverse-mapping function on the componentC_(1,pre) ¹:

=IMF(C _(1,pre) ¹)

where IMF is the functional inverse of the mapping function MF. Thevalues of the reconstructed component

belong thus to the dynamic range of the values of the component C₁ ¹.

In step 201, the components C₁₂ ² and C₁₂ ³ are derived by correctingthe components C₁ ² and C₁ ³ representing the chroma of the input imageas function of the component C_(1,pre) ¹ and the reconstructed component

.

This step 201 allows to control the colors obtained from the threecomponents {C₁₂ ^(m)} and guarantees their perceptual matching to thecolors of the input image. The correction of the components C₁ ² and C₁³ (usually denoted chroma components) may be maintained under control bytuning the parameters of the chroma correcting and inverse mappingsteps. The color saturation and hue obtained from the three components{C₁₂ ^(m)} are thus under control. Such a control is not possible,usually, when a non-parametric mapping function (step 200) is used.

Optionally, in step 203, the component C_(1,pre) ¹ may be adjusted tofurther control the perceived saturation, as follows:C ₁₂ ¹ =C _(1,pre) ¹−max(0,a·C ₁₂ ² +b·C ₁₂ ³)where a and b are two parameters.

This step 203 allows to control the luminance (represented by thecomponent C₁₂ ¹) to guarantee the perceived color matching between thecolors (saturation and hue) obtained from the three components {C₁₂^(m)} and the colors of the input image. The set of parameters SP maycomprise information data relative to the mapping function or itsinverse (steps 200, 202 and 282), information data relative to thechroma correcting (steps 201 and 281), information relative to thesaturation adjusting function, in particular their parameters a and b(steps 203 and 280), and information relative to the conversion used inthe format adapting stages 21, 22, 27, 29 (e.g. gamut mapping and/orinverse gamut mapping parameters).

For example, the control parameters relative to the function TM and/orITM may be determined as specified in Clause C.2.2 (ETSI technicalspecification TS 103 433-1 V1.2.1) and the chroma correcting functionpc) and their parameters may be determined as specified in Clause C.2.3and C.3.4 (ETSI technical specification TS 103 433-1 V1.2.1),

Examples of numerical values of the parameters of the set of parametersSP may be found, for example, in Annex F (Table F.1) (ETSI technicalspecification TS 103 433-1 V1.2.1).

The set of parameters SP may also comprise the information data ID andinformation characteristics of the three components {C₃₀ ^(m)} (steps 29of FIGS. 2 and 3, 284 of FIG. 3).

In more details, the post-processing step 28 comprises steps 280-282which take as input at least one parameter of the set of parameters SP.

In optional step 280, the component CZ of the three components {C₂^(m)}, output of step 27, may be adjusted as follows:C _(2,post) ¹ =C ₂ ¹+max(0,a·C ₂ ² +b·C ₂ ³)

where a and b are two parameters of the set of parameters SP.

For example, the step 280 is executed when the information data IDindicates that SL-HDR1 has to be considered and not executed when itindicates that SL-HDR2 has to be considered.

In step 282, the component C₃ ¹ of the three components {C₃ ^(m)} isobtained by applying a mapping function on the component CZ or,optionally, C_(2,post) ¹:C ₃ ¹=IFM(C _(2,post) ¹)

where ITM is an inverse mapping function derived from at least oneparameter of the set of parameters SP.

In step 281, the components C₃ ², C₃ ³ of the three components {C₃ ^(m)}are derived by inverse correcting the components C₂ ², C₂ ³ of the threecomponents {C₂ ^(m)} according to the component C₂ ¹ or, optionally,C_(2,post) ¹.

According to an embodiment, the components C₂ ² and C₂ ³ are multipliedby a chroma correcting function β(·) as defined by parameters of the setof parameters SP and whose value depends on the component C₂ ¹ or,optionally, C_(2,post) ¹.

Mathematically speaking, the components C₃ ², C₃ ³ are given by:

$\begin{bmatrix}C_{3}^{2} \\C_{3}^{3}\end{bmatrix} = {{\beta\left( C_{2}^{1} \right)}\begin{bmatrix}C_{2}^{2} \\C_{2}^{3}\end{bmatrix}}$

-   -   or optionally,

$\begin{bmatrix}C_{3}^{2} \\C_{3}^{3}\end{bmatrix} = {{\beta\left( C_{2,{{pos}t}}^{1} \right)}\begin{bmatrix}C_{2}^{2} \\C_{2}^{3}\end{bmatrix}}$

FIG. 3 represents a hardware-friendly optimization of single layer-basedsolution of FIG. 2. Said optimization includes two additional steps 283and 284 and allows to reduce complexity for hardware implementation byreducing buses bitwidth use.

In step 283, three components denoted (R₁, G₁, B₁) are obtained fromcomponents C_(3,post) ² and C_(3,post) ³, outputs of the step 281, bytaking into account parameters of the set of parameters SP:

$\begin{bmatrix}R_{1} \\G_{1} \\B_{1}\end{bmatrix} = {\begin{bmatrix}1 & 0 & m_{0} \\1 & m_{1} & m_{2} \\1 & m_{3} & 0\end{bmatrix} \times \begin{bmatrix}S_{0} \\C_{3,{post}}^{2} \\C_{3,{{pos}t}}^{3}\end{bmatrix}}$

where m₀, m₁, m₂, m₃ are parameters of the set of parameters SP and S₀is derived from the components C_(3,post) ² and C_(3,post) ³ and otherparameters of the set of parameters SP.

Parameters m₀, m₁, m₂, m₃ and S₀ may be determined as defined in Clause6.3.2.6 (ETSI technical specification TS 103 433-1 V1.2.1) and their usefor reconstruction may be determined as defined in Clause 7.2.4 (ETSItechnical specification TS 103 433-1 V1.2.1 and ETSI technicalspecification TS 103 433-2 V1.1.1).

In step 284, the three components {C₃ ^(m)} are then obtained by scalingthe three components (R₁, G₁, B₁) according to a component C_(3,post) ¹,output of step 282.

$\left\{ {\begin{matrix}{C_{3}^{1} = {C_{3,{{pos}t}}^{1} \times R_{1}}} \\{C_{3}^{2} = {C_{3,{{pos}t}}^{1} \times G_{1}}} \\{C_{3}^{3} = {C_{3,{{pos}t}}^{1} \times B_{1}}}\end{matrix}\quad} \right.$

where C_(3,post) ¹=IMF(C_(2,post) ¹) (step 282).

For example, the control parameters relative to the mapping function MFand/or its inverse IMF may be determined as specified in Clause C.3.2(ETSI technical specification TS 103 433-1 V1.2.1). The chromacorrecting function β(·) and their parameters may be determined asspecified in Clause C.2.3 and C.3.4 (ETSI technical specification TS 103433-1 V1.2.1). Information data relative to the control parametersrelative to the mapping functions or their inverse and information datarelative to the chroma correcting function β(·) and their parameters areelements of the set of parameters SP. Examples of numerical values ofthe parameters of the set of parameters SP may be found, for example, inAnnex F (Table F.1) (ETSI technical specification TS 103 433-1 V1.2.1.

The parameters m₀, m₁, m₂, m₃ and S₀ may be determined as specified inClause 6.3.2.6 (matrixCoefficient[i] are defining m₀, m₁, m₂, m₃) andClause 6.3.2.8 (kCoefficient[i] are used to construct S₀) of ETSItechnical specification TS 103 433-1 V1.2.1 and their use forreconstruction may be determined as specified in Clause 7.2.4 (ETSItechnical specification TS 103 433-1 V1.2.1).

The mapping function MF(·) is based on a perceptual transfer function,whose goal is to convert a component of an input image into a componentof an output image, thus reducing (or increasing) the dynamic range ofthe values of their luminance. The values of a component of the outputimage belong thus to a lower (or greater) dynamic range than the valuesof the component of an input image. Said perceptual transfer functionuses a limited set of control parameters.

According to a first exemplary embodiment of the end-to-end workflow ofFIG. 2 or FIG. 3, the information data ID indicates that SL-HDR1 has tobe considered.

According to a first variant of said first exemplary embodiment, thecomponent C₁ ¹ is a non-linear signal, denoted luma in literature, whichis obtained (step 21) from the gamma-compressed RGB components of theinput image by:

$C_{1}^{1} = {A_{1}\begin{bmatrix}R^{1/\gamma} \\G^{1/\gamma} \\B^{1/\gamma}\end{bmatrix}}$

Next, according to said first variant, the second and third componentare then obtained (step 21), by applying a gamma compression to the RGBcomponents of the input image:

$\begin{bmatrix}C_{1}^{2} \\C_{1}^{3}\end{bmatrix} = {\begin{bmatrix}A_{2} \\A_{3}\end{bmatrix}\begin{bmatrix}R^{1/\gamma} \\G^{1/\gamma} \\B^{1/\gamma}\end{bmatrix}}$where γ may be a gamma factor, preferably equal to 2.4 and A=[A₁ A₂A₃]^(T) being the canonical 3×3 R′G′B′-to-Y′CbCr conversion matrix (e.g.Recommendation ITU-R BT.2020-2 or Recommendation ITU-R BT.709-6depending on the color space), A₁, A₂, A₃ being 1×3 matrices.

Next, according to said first variant, the second and third componentsC₁ ² and C₁ ³ are chroma corrected from the ratio between the firstcomponent C_(1,pre) ¹ over the reconstructed component

:

$\begin{bmatrix}C_{12}^{2} \\C_{12}^{3}\end{bmatrix} = {\frac{c_{1,{pre}}^{1}}{\Omega.} \cdot \begin{bmatrix}C_{1}^{2} \\C_{1}^{3}\end{bmatrix}}$

where Ω is a constant value either depending on the color primaries ofthe three components {C₁ ^(m)} (equals to 1.2 for Rec. BT.2020 forexample) or being a parameter of the set of parameters SP

Finally, according to said first variant, the three components {C₁₂^(m)} may then be represented as a Y′CbCr 4:2:0 gamma transfercharacteristics video signal.

According to a second variant of said first exemplary embodiment, thecomponent C₁ ¹ of the input image is a linear-light luminance componentL obtained from the RGB component of the input image I₁ by:

$C_{1}^{1} = {L = {A_{1}\begin{bmatrix}R \\G \\B\end{bmatrix}}}$

Next, according to said second variant, the second and third componentare then derived by applying a gamma compression to the RGB componentsof the input image

$\begin{bmatrix}C_{1}^{2} \\C_{1}^{3}\end{bmatrix} = {\begin{bmatrix}A_{2} \\A_{3}\end{bmatrix}\begin{bmatrix}R^{1/\gamma} \\G^{1/\gamma} \\B^{1/\gamma}\end{bmatrix}}$

Next, according to said second variant, the second and third componentC₁₂ ², C₁₂ ³ are then derived (step 201) by correcting the first andsecond components C₁ ², C₁ ³ from the ratio between the first componentC_(1,pre) ¹ over the gamma-compressed reconstructed component

.

[ C 1 ⁢ 2 2 C 1 ⁢ 2 3 ] = C 1 , pre 1 1 / γ ⁡ [ C 1 2 C 1 3 ]

According to a second exemplary embodiment of the end-to-end workflow ofFIG. 2 or FIG. 3, the information data ID indicates that SL-HDR2 has tobe considered.

The three components {C₁ ^(m)} may then be represented as a Y′CbCr 4:4:4full range PQ10 (PQ 10 bits) video signal (specified in Rec. ITU-RBT.2100). The three components {C₂₀ ^(m)}, which is an PQ 10-bits imagedata and associated metadata computed from the three components {C₁^(m)} (typically 10, 12 or 16 bits), are provided, and said PQ 10-bitsimage data is then encoded (step 23) using, for example an HEVC Main 10profile encoding scheme.

Next, according to said second variant, the second and third componentC₁₂ ², C₁₂ ³ are then derived (step 201) by correcting the first andsecond components C₁ ², C₁ ³ from the ratio between the first componentC_(1,pre) ¹ over the reconstructed component

.

According to a first variant of said second exemplary embodiment, thethree components {C₃₀ ^(m)} are directly obtained from the three decodedcomponents {

}.

According to a second variant of said second exemplary embodiment, inthe post-processing step 28, three components {C₃₀ ^(m)} arereconstructed from the three decoded components {

} and the set of parameters SP (step 25).

The three components {C₃₀ ^(m)} are then available for either an SDR orHDR enabled CE display. The format of the image I₃ is possibly adapted(step 29) as explained above. The mapping function TM of FIGS. 2 and 3is based on a perceptual transfer function, whose goal is to convert acomponent of an input image I₁ into a component of an image I₁₂, thusreducing (or increasing) the dynamic range of the values of theirluminance. The values of a component of an image I₁₂ belong thus to alower (or greater) dynamic range than the values of the component of aninput image I₁. Said perceptual transfer function uses a limited set ofcontrol parameters.

FIG. 4a shows an illustration of a perceptual transfer function TM whichmay be used for mapping luminance components but a similar perceptualtransfer function for mapping the luminance component may be used. Themapping is controlled by a mastering display peak luminance parameter(equal to 5000 cd/m² in FIG. 4a ). To better control the black and whitelevels, a signal stretching between content-dependent black and whitelevels is applied. Then the converted signal is mapped using apiece-wise curve constructed out of three parts, as illustrated in FIG.4b . The lower and upper sections are linear, the steepness beingdetermined by the shadowGain control and highlightGain controlparameters respectively. The mid-section is a parabola providing acontinuous and smooth bridge between the two linear sections. The widthof the cross-over is determined by the midToneWidthAdjFactor parameter.All the parameters controlling the mapping may be conveyed as metadatafor example by using a SEI message as specified in ETSI TS 103 433-1Annex A.2 metadata.

FIG. 4c shows an example of the inverse of the perceptual transferfunction TM (FIG. 4a ) to illustrate how a perceptually optimizedluminance signal may be converted back to the linear-light domain basedon a targeted legacy display maximum luminance, for example 100 cd/m².

In step 25 (FIG. 2 or 3), the set of parameters SP is obtained toreconstruct the three components {C₃ ^(m)} from the three components {

}. These parameters may be obtained from metadata obtained from abitstream, for example the bitstream B.

ETSI TS 103 433-1 V1.2.1 clause 6 and Annex A.2 provide an example ofsyntax of said metadata. The syntax of this ETSI recommendation isdescribed for reconstructing an HDR video from an SDR video but thissyntax may extend to the reconstruction of any image from any decodedcomponents; as an example, TS 103 433-2 V1.1.1 uses the same syntax forreconstructing a display adapted HDR video from an HDR video signal(with a different dynamic range).

According to ETSI TS 103 433-1 V1.2.1, said dynamic metadata may beconveyed according to either a so-called parameter-based mode or atable-based mode. The parameter-based mode may be of interest fordistribution workflows which primary goal is to provide direct SDRbackward compatible services with very low additional payload orbandwidth usage for carrying the dynamic metadata. The table-based modemay be of interest for workflows equipped with low-end terminals or whena higher level of adaptation is required for representing properly bothHDR and SDR streams. In the parameter-based mode, dynamic metadata to beconveyed are luminance mapping parameters representative of the inversemapping function to be applied at the post-processing step, i.e.tmInputSignalBlackLevelOffset, tmInputSignalWhiteLevelOffset,shadowGain; highlightGain; midToneWidthAdjFactor; tmOutputFineTuningparameters.

Moreover, other dynamic metadata to be conveyed are color correctionparameters (saturationGainNumVal, saturationGainX(i) andsaturationGainY(i)) used to fine-tune the default chroma correctingfunction β(·) as specified in ETSI TS 103 433-1 V1.2.1 clauses 6.3.5 and6.3.6. The parameters a and b may be respectively carried in thesaturationGain function parameters as explained above. These dynamicmetadata may be conveyed using the HEVC SL-HDR Information (SL-HDRI)user data registered SEI message (see ETSI TS 103 433-1 V1.2.1 AnnexA.2) or another extension data mechanism such as specified in theAVS2/IEEE1857.4 specification. Typical dynamic metadata payload size isless than 100 bytes per picture or scene.

Back to FIG. 3, in step 25, the SL-HDRI SEI message is parsed to obtainat least one parameters of the set of parameters SP.

In step 282 and 202, the inverse mapping function ITM (so-calledlutMapY) is reconstructed (derived) from the obtained mapping parameters(see ETSI TS 103 433-1 V1.2.1 clause 7.2.3.1 for more details, —sameclause for TS 103 433-2 V1.1.1).

In step 282 and 202, the chroma correcting function β(·) (so-calledlutCC) is also reconstructed (derived) from the obtained colorcorrection parameters (see ETSI TS 103 433-1 V1.2.1 clause 7.2.3.2 formore details, same clause for TS 103 433-2 V1.1.1).

In the table-based mode, dynamic data to be conveyed are pivots pointsof a piece-wise linear curve representative of the mapping function. Forexample, the dynamic metadata are luminanceMappingNumVal that indicatesthe number of the pivot points, luminanceMappingX that indicates theabscissa (x) values of the pivot points, and luminanceMappingY thatindicates the ordinate (y) values of the pivot points (see ETSI TS 103433-1 V1.2.1 clauses 6.2.7 and 6.3.7 for more details). Moreover, otherdynamic metadata to be conveyed may be pivots points of a piece-wiselinear curve representative of the chroma correcting function pc). Forexample, the dynamic metadata are colorCorrectionNumVal that indicatesthe number of pivot points, colorCorrectionX that indicates the x valuesof pivot points, and colorCorrectionY that indicates the y values of thepivot points (see ETSI TS 103 433-1 V1.2.1 clauses 6.2.8 and 6.3.8 formore details). These dynamic metadata may be conveyed using the HEVCSL-HDRI SEI message (mapping between clause 6 parameters and annex Adistribution metadata is provided in Annex A.2.3 of ETSI TS 103 433-1V1.2.1).

In step 25, the SL-HDRI SEI message is parsed to obtain the pivot pointsof a piece-wise linear curve representative of the inverse mappingfunction and the pivot points of a piece-wise linear curverepresentative of the chroma correcting function pc), and the chroma toluma injection parameters a and b.

In step 282 and 202, the inverse mapping function is derived from thosepivot points relative to a piece-wise linear curve representative of theinverse mapping function ITM (see ETSI TS 103 433-1 V1.2.1 clause7.2.3.3 for more details,—same clause for ETSI TS 103 433-2 V1.1.1).

In step 281 and 201, the chroma correcting function pc), is also derivedfrom those of said pivot points relative to a piece-wise linear curverepresentative of the chroma correcting function pc), (see ETSI TS 103433-1 V1.2.1 clause 7.2.3.4 for more details, —same clause for TS 103433-2 V1.1.1).

Note that static metadata also used by the post-processing step may beconveyed by SEI message. For example, the selection of either theparameter-based mode or table-based mode may be carried by thepayloadMode information as specified by ETSI TS 103 433-1 V1.2.1 (clauseA.2.2). Static metadata such as, for example, the color primaries or themaximum display mastering display luminance are conveyed by a

Mastering Display Colour Volume (MDCV) SEI message as specified in AVC,HEVC or embedded within the SL-HDRI SEI message as specified in ETSI TS103 433-1 V1.2.1 Annex A.2.

According to an embodiment of step 25, the information data ID isexplicitly signaled by a syntax element in a bitstream and thus obtainedby parsing the bitstream. For example, said syntax element is a part ofan SEI message such as sl_hdr_mode_value_minus1 syntax element containedin SL-HDRI SEI message.

According to an embodiment, said information data ID identifies what isthe processing applied to the input image I₁ to process the set ofparameters SP. According to this embodiment, the information data ID maythen be used to deduce how to use the parameters to reconstruct thethree components {C₃ ^(m)} (step 25).

For example, when equal to 1, the information data ID indicates that theset of parameters SP has been obtained by applying the SL-HDR1pre-processing step (step 20) to an input image and that the threedecoded components {

} form an SDR image. When equal to 2, the information data ID indicatesthat the parameters have been obtained by applying the SL-HDR2pre-processing step (step 20) to an HDR 10 bits image (input of step20), that the three decoded components {

} are an HDR10 image, and the inverse mapping function ITM function maybe composed by a PQ transfer function (or its inverse).

Medium Dynamic Range (MDR) distribution corresponds to a use caseextracted during DVB Dynamic Mapping Information (a.k.a. DMI) (i.e. HDRdynamic metadata) standardization phase. Typically, an MDR display (suchas qualified in this document) is an HDR display characterized by a peakluminance of several hundreds of cd/m² (e.g. 500 cd/m²) while an HDRdisplay (such as referenced in this document) ranges with a peakluminance from a thousand to several thousands of cd/m² (e.g. 1000 or2000 cd/m²). Especially HDR peak luminance is greater than MDR peakluminance.

Indeed, it is of uttermost interest for the operator to ensure thehighest possible quality in terms of image rendition for its clients.Thus, MDR distribution appears as a first step to broadcast a signalwhich fits consumer displays in “average”.

FIG. 6 represents an MDR distribution use case. In the figure, a sourcesignal HDR_(s) is converted by a pre-processing block 60 to a MediumDynamic Range signal MDR, which is distributed over a network NET suchas mentioned above. At the receiving end, the Medium Dynamic Rangesignal MDR is, depending on the peak luminance of the presentationdisplay L_(pdisp) of the connected display, either down-mapped in block61 to an HDR⁻ or SDR signal or up-mapped in block 62 to an HDR⁺ signal.The “HDR (>MDR) rendering” 64 of the HDR⁺ signal is performed by ahigh-end TV with superior processing and peak luminance, while “HDR(<MDR)/SDR rendering” 63 of the HDR⁻ signal is performed by entry-levelto mid-range displays. HDR/MDR signals are typically distributed withPQ10 signal coding (see. Rec. ITU-R BT.2100 [3]). For simplification'ssake, coding/decoding stages does not appear on the scheme. Furthermore,the display adaptation, a.k.a. display mapping, processing 61, 62 may beembedded in a display with the rendering or they can be set outside thedisplay in a source device (e.g. STB).

The idea behind this use case is that the content distributors broadcastan HDR signal with an intermediary dynamic range MDR signal which ismore representative of the majority of deployed HDR displayscharacteristics than the original HDRs signal mastered on a high-endmastering display with superior dynamic range. As the operator controlsthe HDR-to-MDR down-conversion 60 upstream of the distribution stage,the quality of the rendering on consumer displays is better preserved asdisplay image processing leeway is minimized. Indeed, display imageprocessing is often performed through statistics of the content to berendered but without any guidance from the content producer—the displayadaptation can be qualified as “blind” unlike display adaptationprocessing driven by (dynamic) metadata carried at least from theemission encoder and which results are controlled by the operator.

Some advantages of MDR distribution are as follows:

-   -   the distributed MDR signal better fits to actual deployed HDR        displays characteristics (less range for signal conversions in        the display);    -   HDR-to-MDR signal is controlled by the operator thus        guaranteeing content artistic intent preservation (critical        especially for vertical market/pay TV operators);    -   the operator may adapt the distributed signal over years to        better match its clients average display characteristics (e.g.        increasing distributed MDR peak luminance when the clients        display fleet peak luminance increases).

Display mapping algorithms are in charge of performing the adaptation ofthe (MDR) signal dynamic range to the displays capabilities. However,the large variety of displays over a wide product range from low-enddevices with cheap processing to high-end system-on-chips embeddinghighly complex image processing modules and various display technologiessuch as LED, OLED or QDOT conduct to important inequality in terms ofcontent rendition. Differences have even recently increased with theadvent of HDR which offer higher differentiation opportunities. Theproblem is that built-in display mapping is largely dependent on thedisplay price range (SoC complexity) and rendering technology. Besides,such “blind” display mapping algorithms (i.e. not guided nor elected byoperator) may not succeed in sticking to the original content artisticintent especially when the display characteristics are very differentfrom those of the mastering display used to grade the content. In thiscase, there are benefits to take advantage of dynamic mapping metadatawhich convey an operator-approved dynamic mapping of the content.

There are two formats for carrying HDR signals: HLG and PQ (see. [3]).Pay TV operators may rather consider PQ when it comes to qualityensuring as the signal is carried throughout the end-to-end video chainwithout compromises on the quality. HLG format proposes built-in displayadaptation but with limitations that may not satisfy pay TV operatorsrequirements in terms of quality (see [3] and [4]). However, thefollowing principles may also apply to display adaptation overHLG-formatted HDR signals.

Considering SL-HDR technologies (ETSI TS 103 433 suite of standards),SL-HDR2 proposes display mapping guided by dynamic metadata for HDRPQ10-coded signals.

This is illustrated in FIG. 7, where at the distribution stage anincoming HDR PQ10-coded signal is analysed by a pre-processing block 70to generate the dynamic metadata SL-HDR2 MD. The HDR signal is convertedinto a Medium Dynamic Range signal MDR by post-processing block 71 anddistributed over distribution network NET with accompanying metadata MD.Also the additional dynamic metadata SL-HDR2 MD are transmitted on thedistribution network, typically by way of the SEI messaging mechanism.

Downstream to the distribution network the MDR signal may be directlyinterpreted by a PQ10 compliant display and the display mapping 72 mayoccur in the display (or upstream to the display e.g. in a sourcereceiver such as a STB, an UltraHD Blu-ray disk player . . . ).Alternatively, the MDR signal accompanied by MDR-to-HDR/SDR metadata(e.g. SL-HDR2 metadata) may be interpreted by a device comprising an“MDR-to-HDR/SDR post-processing” block 73 (e.g. an STB or a TVintegrating an SL-HDR2 post-processor) to reconstruct a display adaptedHDR or SDR signal. This block 73 may be directly embedded in thepresentation display or set apart in a source device (e.g. STB) whichdispatches the display adapted/reconstructed signal to the presentationdisplay for HDR/SDR rendering 74.

Annex H “Minimum and maximum value of Lpdisp for display adaptation” ofthe SL-HDR2 specification ([2]) provides recommendations on presentationdisplay peak luminance range for which SL-HDR2 display mapping may beused. As mentioned there, in case Lpdisp is anywhere in between 100cd/m² and the maximum luminance of the HDR grading monitor,hdrDisplayMaxLuminance (clause 6.2.3 in [1]), the metadata recomputationfor display adaptation of clause 7.3 is in effect an interpolation. Itis possible to recompute the metadata using the same procedure of clause7.3 to perform display adaptation for a presentation display with avalue of Lpdisp that is higher than the maximum luminance of the HDRgrading monitor. Because this is now an extrapolation, care should betaken not to use values for Lpdisp that are too high. This clause offersa recommendation for the lower and upper boundary of Lpdisp for applyingthe procedure of clause 7.3 for display adaptation. Display adaptationshould not be used for a value of Lpdisp lower than Lpdisp_min or higherthan Lpdisp_max, see the following equations

     L_(pdisp_min) = 100  cd/m 2 $L_{pdisp\_ max} = \begin{matrix}{{L_{HDR} \times 2},} & {{{if}\mspace{14mu} L_{HDR}} \leq {1000\mspace{14mu}{{cd}/m^{2}}}} \\{{{Min}\left( {{{Max}\left( {{L_{HDR} \times 1},{25;{2\mspace{11mu} 000}}} \right)};10000} \right)},} & {otherwise}\end{matrix}$where:L_(HDR) is the HDR mastering display maximum luminancehdrDisplayMaxLuminance.

A S-LHDR-2 solution for addressing MDR signals is schematically shown inFIG. 8, wherein the peak luminance for the HDR_(s), MDR, HDR, and HDR₂signals could be for example as follows:LHDR_(s)>500 cd/m²LMDR=500 cd/m²LHDR₁>500 cd/m²LHDR₂<500 cd/m²

Similar to FIG. 7, an incoming PQ10-coded signal HDR_(s) is analysed bya pre-processing block 80 to generate dynamic metadata MD₁. The HDRsignal is converted into a Medium Dynamic Range signal MDR bypost-processing block 81.

Downstream to the distribution network the MDR signal is adapted to thepeak luminance of the presentation display. In case of a HDR display 83with a maximum luminance value LHDR, the peak luminance value of thepresentation display L_(pdisp1) is supplied to the “Post-proc SL-HDR2”block 82 which performs an up-mapping of the distributed MDR signal byextrapolation. On the other hand, for rendering the received signal on aSDR/HDR display 85 with a maximum luminance value LHDR₂, a down-mappingof the distributed MDR signal via interpolation is performed by the“Post-proc SL-HDR2” block 84 in response to the peak luminance value ofthe presentation display L_(pdisp2).

This SL-HDR2 solution is well designed for addressing presentationdisplays which peak luminance is lower than the peak luminance of thetransmitted MDR signal. However, although current SL-HDR2 technologypermits to extrapolate the MDR peak luminance signal to a higher HDRpeak luminance (e.g. considering a premium TV sets with a peak luminancebeyond 1000 cd/m²), the extrapolated signal does not take into accountthe original source HDR signal (upstream to the HDR-to-MDRpre-processing module at the emission encoder side) thus such a displayadapted signal may deviate from the original signal intent. The presentembodiments propose a solution to circumvent this limitation of theSL-HDR2 design for MDR signals, wherein the following principles mayapply to HLG-based technology.

The ETSI TS 103 433 (SL-HDR) suite of standards—comprising part 1specifying SL-HDR1 and part 2 specifying SL-HDR2—implementspre-processing and post-processing modules. The pre-processing modulegenerates metadata (operator-approved) and the post-processing moduleapplies metadata to a signal in order to reconstruct another signal. Thepost-processing module is implemented in consumer equipment as a uniquehardware block so that this same hardware block is used to interpretSL-HDR1 and SL-HDR2 signals: the SL-HDR post-processor. The SL-HDRmetadata are also common to part 1 and 2.

The global idea of the present embodiments is to leverage either SL-HDR2post-processor for down-mapping the MDR signal or SL-HDR1 post-processorfor up-mapping the MDR signal by reusing this existing common hardwaremodule (present in consumer electronics devices implementing SL-HDRpost-processor) and reconfiguring to either SL-HDR1 or SL-HDR2 mode toreply to the current limitations.

The corresponding SL-HDR post-processor logic modification is shown inFIG. 9. Typically, pre-distribution stages 80 and 81 are identical tothe ones previously described in the context of FIG. 8. In particular,the SL-HDR2 metadata are generated once by the SL-HDR2 pre-processor andthen, a SL-HDR2 post-processor is applying computed metadata to performthe HDR-to-MDR conversion (i.e. actually operating an SL-HDR2 displaymapping process prior to the distribution stage). Afterwards, the MDRsignal and SL-HDR metadata are transmitted on the distribution network.

After the distribution network, the SL-HDR post-processor, which can beintegrated in a consumer electronic device, is changed as shown in FIG.10:

-   -   1) In a first step 10 the SL-HDR post-processor receives:        -   a) the MDR signal        -   b) the MDR-to-HDR/SDR (SL-HDR) metadata        -   c) (at least) the peak luminance of the presentation display            (L_(pdisp))        -   (e.g. through EDID—See CTA-861.3/CTA-861-G [5])    -   2) The SL-HDR post-processor determines in a following step 11        whether the peak luminance of the MDR signal (L_(MDR)) is        greater or lower than the peak luminance of the presentation        display (L_(pdisp)) which the MDR signal should be adapted to.    -   3) Metadata application in SL-HDR post-processor:        -   a) If (L_(MDR)>L_(pdisp)) then SL-HDR2 post-processor is            used in step 12 for application on SL-HDR2 metadata        -   b) Otherwise (if L_(MDR)≤L_(pdisp)) then a modified SL-HDR1            post-processor is used in step 13 for application on SL-HDR2            metadata rather than using extrapolation of SL-HDR2            metadata.

It is to be noted that alike SL-HDR post-processor hardware, SL-HDRmetadata are common to SL-HDR1 and 2.

According to an embodiment, the common SL-HDR post-processor (i.e.common to SL-HDR1 or 2) usually enters a specific mode (SL-HDR1 or 2)responsive to the field sl_hdr_mode_value_minus1 (matching with thePartID variable) of the SL-HDR dynamic metadata specified in Annex A of[1]. The value of this field is overwritten according to the logicdepicted in FIG. 10 (case 3) b) above). Additionally, when the field isoverwritten in the SL-HDR post-processor, the SL-HDR1 post-processor ismodified (adapted) as explained below.

Adaptations to be operated on the input of SL-HDR1 post-processor aretwofold:

-   -   The SL-HDR1 post-processor conventional input is a signal        encoded with gamma transfer function and not PQ (or HLG) and    -   The SL-HDR1 post-processor conventional input is an SDR signal        (whose peak luminance is assumed to be 100 cd/m²) and not the        peak luminance of an HDR/MDR signal (typically over 100 cd/m²).

Thus, in the processing of the MDR signal by the modified SL-HDR1post-processor, the processing specified in clause 7.2.3.1.3 (block “Toperceptual uniform signal”) of TS 103 433-1 [1] is replaced byprocessing specified in clause 7.2.3.1.3 (block “To perceptual uniformsignal”) of TS 103 433-2 [2] so that SL-HDR1 could linearize an HDR PQsignal (in which the MDR signal is represented) rather than an SDR(gamma-encoded) signal. The processing specified in clause 7.2.3.1.3 ispart of step 282 in FIGS. 2 and 3.

Similarly, processing block specified in clause 7.2.3.1.9 (block“Inverse EOTF”) of [1] is replaced by processing block specified in7.2.3.1.9 of [2]. The processing specified in clause 7.2.3.1.9 is partof step 282 in FIGS. 2 and 3.

Besides, L_(SDR) representing the maximum display mastering luminance ofan SDR mastering display of 100 cd/m² should be set to the maximumluminance (or peak luminance) of the MDR signal in any relevant portionof [1] i.e. whenever L_(SDR) appears in the specification it should bereplaced by L_(MDR) in the whole document.

For instance, this information is retrieved thanks to the fieldcoded_picture_max_luminance set when coded_picture_info_present_flag isset to 1.

Alternatively, information can be obtained from targetpicture_max_luminance field. These fields are specified in Annex A of[1].

In a variant, chroma_to_luma_injection[i] and k_coefficient[j]parameters values which are fixed to 0 for SL-HDR2 are changed whenSL-HDR1 post-processor is used i.e. when SL-HDR post-processor isconfigured in an SL-HDR1 post-processor mode to up-map the MDR signal.

As an example, these values are defaulted to recovery mode values suchas described in Table F.1 in annex F of TS 103 433-1.

Some advantages of the embodiments are as follows:

-   -   Using SL-HDR1 post-processing for up-mapping of a MDR signal        improves rendition of the reconstructed HDR signal over SL-HDR2        post-processing as SL-HDR1 natively up-maps signals while        SL-HDR2 natively down-maps signals by design (no extrapolation        of the MDR signal but considering the original signal peak        luminance prior to its MDR down-conversion), thus resulting in        optimal usage of the SL-HDR post-processor.    -   The solution could be deployed as a firmware update for        SL-HDR-enabled consumer products already on the market.

On FIG. 1-4 c, 6-10, the modules are functional units, which may or notbe in relation with distinguishable physical units. For example, thesemodules or some of them may be brought together in a unique component orcircuit or contribute to functionalities of a software. A contrario,some modules may potentially be composed of separate physical entities.The apparatus which are compatible with the present principles areimplemented using either pure hardware, for example using dedicatedhardware such ASIC or FPGA or VLSI, respectively «Application SpecificIntegrated Circuit», «Field-Programmable Gate Array», «Very Large ScaleIntegration», or from several integrated electronic components embeddedin a apparatus or from a blend of hardware and software components.

FIG. 5 represents an exemplary embodiment of an architecture of aapparatus 50 which may be configured to implement a method described inrelation with FIG. 1 to FIG. 4c , 6-10.

Apparatus 50 comprises following elements that are linked together by adata and address bus 51: a microprocessor 52 (or CPU), which is, forexample, a DSP (or Digital Signal Processor), a ROM (or Read OnlyMemory) 53, a RAM (or Random Access Memory) 54, an I/O interface 55 forreception of data to transmit, from an application and optionally abattery 56. In accordance with an example, the battery 56 is external tothe apparatus. In each of mentioned memory, the word «register» used inthe specification can correspond to area of small capacity (some bits)or to very large area (e.g. a whole program or large amount of receivedor decoded data). The ROM 53 comprises at least a program andparameters. The ROM 53 may store algorithms and instructions to performtechniques in accordance with present principles. When switched on, theCPU 52 uploads the program in the RAM 54 and executes the correspondinginstructions. RAM 54 comprises, in a register, the program executed bythe CPU 52 and uploaded after switch on of the apparatus 50, input datain a register, intermediate data in different states of the method in aregister, and other variables used for the execution of the method in aregister.

The implementations described herein may be implemented in, for example,a method or a process, an apparatus, a software program, a data stream,or a signal. Even if only discussed in the context of a single form ofimplementation (for example, discussed only as a method or a apparatus),the implementation of features discussed may also be implemented inother forms (for example a program). An apparatus may be implemented in,for example, appropriate hardware, software, and firmware. The methodsmay be implemented in, for example, an apparatus such as, for example, aprocessor, which refers to processing apparatuses in general, including,for example, a computer, a microprocessor, an integrated circuit, or aprogrammable logic apparatus. Processors also include communicationapparatuses, such as, for example, computers, cell phones,portable/personal digital assistants (“PDAs”), and other apparatusesthat facilitate communication of information between end-users.

In accordance with an example, the input video or an image of an inputvideo is obtained from a source. For example, the source belongs to aset comprising a local memory (53 or 54), e.g. a video memory or a RAM(or Random Access Memory), a flash memory, a ROM (or Read Only Memory),a hard disk, a storage interface (55), e.g. an interface with a massstorage, a RAM, a flash memory, a ROM, an optical disc or a magneticsupport, a communication interface (55), e.g. a wireline interface (forexample a bus interface, a wide area network interface, a local areanetwork interface) or a wireless interface (such as a IEEE 802.11interface or a Bluetooth® interface); and an image capturing circuit(e.g. a sensor such as, for example, a CCD (or Charge-Coupled Device) orCMOS (or Complementary Metal-Oxide-Semiconductor)).

In accordance with examples, the bitstream carrying on the metadata issent to a destination. As an example, a bitstream is stored in a localor remote memory, e.g. a video memory or a RAM (54), a hard disk. In avariant, at least one of the bitstreams is sent to a storage interface(55), e.g. an interface with a mass storage, a flash memory, ROM, anoptical disc or a magnetic support and/or transmitted over acommunication interface (55), e.g. an interface to a point to pointlink, a communication bus, a point to multipoint link or a broadcastnetwork.

In accordance with other examples, the bitstream carrying on themetadata is obtained from a source. Exemplarily, the bitstream is readfrom a local memory, e.g. a video memory (54), a RAM (54), a ROM (53), aflash memory (53) or a hard disk (53). In a variant, the bitstream isreceived from a storage interface (55), e.g. an interface with a massstorage, a RAM, a ROM, a flash memory, an optical disc or a magneticsupport and/or received from a communication interface (55), e.g. aninterface to a point to point link, a bus, a point to multipoint link ora broadcast network.

In accordance with examples, apparatus 50 being configured to implementthe method as described above, belongs to a set comprising a mobiledevice, a communication device, a game device, a tablet (or tabletcomputer), a laptop, a still image camera, a video camera, anencoding/decoding chip, a television, a set-top-box, a display, a stillimage server and a video server (e.g. a broadcast server, avideo-on-demand server or a web server).

Implementations of the various processes and features described hereinmay be embodied in a variety of different equipment or applications.Examples of such equipment include an encoder, a decoder, apost-processor processing output from a decoder, a pre-processorproviding input to an encoder, a video coder, a video decoder, a videocodec, a web server, a set-top box, a laptop, a personal computer, acell phone, a PDA, and any other device for processing an image or avideo or other communication apparatuses. As should be clear, theequipment may be mobile and even installed in a mobile vehicle.

Additionally, the methods may be implemented by instructions beingperformed by a processor, and such instructions (and/or data valuesproduced by an implementation) may be stored on a computer readablestorage medium. A computer readable storage medium can take the form ofa computer readable program product embodied in one or more computerreadable medium(s) and having computer readable program code embodiedthereon that is executable by a computer. A computer readable storagemedium as used herein is considered a non-transitory storage mediumgiven the inherent capability to store the information therein as wellas the inherent capability to provide retrieval of the informationtherefrom. A computer readable storage medium can be, for example, butis not limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. It is to be appreciated that thefollowing, while providing more specific examples of computer readablestorage mediums to which the present principles can be applied, ismerely an illustrative and not exhaustive listing as is readilyappreciated by one of ordinary skill in the art: a portable computer; afloppy disk; a hard disk; a read-only memory (ROM); an erasableprogrammable read-only memory (EPROM or Flash memory); a portablecompact disc read-only memory (CD-ROM); an optical storage device; amagnetic storage device; or any suitable combination of the foregoing.

The instructions may form an application program tangibly embodied on aprocessor-readable medium. Instructions may be, for example, inhardware, firmware, software, or a combination. Instructions may befound in, for example, an operating system, a separate application, or acombination of the two. A processor may be characterized, therefore, as,for example, both a apparatus configured to carry out a process and aapparatus that includes a processor-readable medium (such as a storageapparatus) having instructions for carrying out a process. Further, aprocessor-readable medium may store, in addition to or in lieu ofinstructions, data values produced by an implementation.

As will be evident to one of skill in the art, implementations mayproduce a variety of signals formatted to carry information that may be,for example, stored or transmitted. The information may include, forexample, instructions for performing a method, or data produced by oneof the described implementations. For example, a signal may be formattedto carry as data the rules for writing or reading the syntax of adescribed example of the present principles, or to carry as data theactual syntax-values written by a described example of the presentprinciples. Such a signal may be formatted, for example, as anelectromagnetic wave (for example, using a radio frequency portion ofspectrum) or as a baseband signal. The formatting may include, forexample, encoding a data stream and modulating a carrier with theencoded data stream. The information that the signal carries may be, forexample, analog or digital information. The signal may be transmittedover a variety of different wired or wireless links, as is known. Thesignal may be stored on a processor-readable medium.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made. For example,elements of different implementations may be combined, supplemented,modified, or removed to produce other implementations. Additionally, oneof ordinary skill will understand that other structures and processesmay be substituted for those disclosed and the resulting implementationswill perform at least substantially the same function(s), in at leastsubstantially the same way(s), to achieve at least substantially thesame result(s) as the implementations disclosed. Accordingly, these andother implementations are contemplated by this application.

REFERENCES

-   [1] ETSI TS 103 433-1 v1.2.1 (2017-08), «High-Performance Single    Layer High Dynamic Range (HDR) System for use in Consumer    Electronics devices; Part 1: Directly Standard Dynamic Range (SDR)    Compatible HDR system (SL-HDR1)”.-   [2] ETSI TS 103 433-2 v1.1.1, «High-Performance Single Layer High    Dynamic Range (HDR) System for use in Consumer Electronics devices;    Part 2: Enhancements for EPRceptual Quantization (PQ) transfer    function based High Dynamic Range (HDR) Systems (SL-HDR-2)”.-   [3] Rec. ITU-R BT.2100-2 (2018-07), “Image parameter values for high    dynamic range television for use in production and international    programme exchange”-   [4] Report ITU-R BT.2390-4, “High dynamic range television for    production and international programme exchange”, (04-2018).-   [5] CTA-861-G, CTA Standard CTA-861-G, November 2016: “A DTV Profile    for Uncompressed High Speed Digital Interfaces”.

The invention claimed is:
 1. A method for processing a video signal,comprising: receiving a medium dynamic range video signal and associatedmetadata, the metadata including data representative of a peak luminancevalue of the medium dynamic range video signal; receiving datarepresentative of a peak luminance value of a presentation display;determining whether the peak luminance value of the medium dynamic rangevideo signal is greater or lower than the peak luminance value of thepresentation display; configuring a processor based on thedetermination, wherein the processor has a first mode to reconstruct ahigh dynamic range video signal based on a received standard dynamicrange video signal and associated metadata, and a second mode tooptimize a received high dynamic range video signal for a renderingdevice; and processing the medium dynamic range video signal by theprocessor in the first mode if the peak luminance value of the mediumdynamic range video signal is smaller than the peak luminance value ofthe presentation display and in the second mode if the peak luminancevalue of the medium dynamic range video signal is greater than the peakluminance value of the presentation display, wherein a variable includedin the metadata has a data value representing the second mode to specifythat a high dynamic range video signal has been pre-processed accordingto the second mode to generate the medium dynamic range video signal. 2.The method according to claim 1, wherein the medium dynamic range videosignal is processed in the first mode for up-mapping the medium dynamicrange video signal and is processed in the second mode for down-mappingthe medium dynamic range video signal.
 3. The method according to claim1, wherein the variable is overwritten with a data value representingthe first mode if the peak luminance value of the medium dynamic rangevideo signal is smaller than the peak luminance value of thepresentation display.
 4. The method according to claim 1, wherein thevariable is a part of an SEI message within the received metadata. 5.The method according to claim 1, wherein the processor is configured toprocess in the first mode a SL-HDR1 signal and in the second mode aSL-HDR2 signal and the variable corresponds to thesl_hdr_mode_value_minus1 syntax element.
 6. The method according toclaim 1, wherein the processor is adapted to linearize the mediumdynamic range video signal in the first mode.
 7. The method according toclaim 1, wherein in the processing according to the first mode aparameter representing a maximum display mastering luminance of astandard dynamic range mastering display is set to the peak luminancevalue of the medium dynamic range video signal.
 8. The method accordingto claim 1, wherein the received medium dynamic range video signal isrepresented as a SL-HDR2 signal and the processor is adapted to processthe received medium dynamic signal in the first mode.
 9. A processor forprocessing a video signal, the processor having a first mode toreconstruct a high dynamic range video signal based on a receivedstandard dynamic range video signal and associated metadata, theprocessor having a second mode to optimize a received high dynamic rangevideo signal for a rendering device, the processor being configured for:receiving a medium dynamic range video signal and associated metadata,the metadata including data representative of a peak luminance value ofthe medium dynamic range video signal; receiving data representative ofa peak luminance value of a presentation display; determining whetherthe peak luminance value of the medium dynamic range video signal isgreater or lower than the peak luminance value of the presentationdisplay; and processing the medium dynamic range video signal in thefirst mode if the peak luminance value of the medium dynamic range videosignal is smaller than the peak luminance value of the presentationdisplay and in the second mode if the peak luminance value of the mediumdynamic range video signal is greater than the peak luminance value ofthe presentation display, wherein a variable included in the metadatahas a data value representing the second mode to specify that a highdynamic range video signal has been pre-processed according to thesecond mode to generate the medium dynamic range video signal.
 10. Anapparatus comprising a processor according to claim
 9. 11. The apparatusaccording to claim 10, further comprising an output for providing theprocessed medium dynamic range video signal to a display device.
 12. Theapparatus according to claim 10, further comprising a display fordisplaying the processed medium dynamic range video signal.
 13. Theprocessor according to claim 9, wherein the medium dynamic range videosignal is processed in the first mode for up-mapping the medium dynamicrange video signal and is processed in the second mode for down-mappingthe medium dynamic range video signal.
 14. The processor according toclaim 9, wherein the variable is overwritten with a data valuerepresenting the first mode if the peak luminance value of the mediumdynamic range video signal is smaller than the peak luminance value ofthe presentation display.
 15. The processor according to claim 9,wherein the variable is a part of an SEI message within the receivedmetadata.
 16. The processor according to claim 9, wherein the processoris configured to process in the first mode a SL-HDR1 signal and in thesecond mode a SL-HDR2 signal and the variable corresponds to thesl_hdr_mode_value_minus1 syntax element.
 17. The processor according toclaim 9, wherein the received medium dynamic range video signal isrepresented as a SL-HDR2 signal and the processor is adapted to processthe received medium dynamic signal in the first mode.
 18. Anon-transitory computer-readable medium comprising instructions thatcause a computer to process a video signal, the processing comprising:receiving a medium dynamic range video signal and associated metadata,the metadata including data representative of a peak luminance value ofthe medium dynamic range video signal; receiving data representative ofa peak luminance value of a presentation display; determining whetherthe peak luminance value of the medium dynamic range video signal isgreater or lower than the peak luminance value of the presentationdisplay; configuring a processor based on the determination, wherein theprocessor has a first mode to reconstruct a high dynamic range videosignal based on a received standard dynamic range video signal andassociated metadata, and a second mode to optimize a received highdynamic range video signal for a rendering device; and processing themedium dynamic range video signal by the processor in the first mode ifthe peak luminance value of the medium dynamic range video signal issmaller than the peak luminance value of the presentation display and inthe second mode if the peak luminance value of the medium dynamic rangevideo signal is greater than the peak luminance value of thepresentation display, wherein a variable included in the metadata has adata value representing the second mode to specify that a high dynamicrange video signal has been pre-processed according to the second modeto generate the medium dynamic range video signal.
 19. Thenon-transitory computer-readable medium according to claim 18, whereinthe received medium dynamic range video signal is represented as aSL-HDR2 signal and the processor is adapted to process the receivedmedium dynamic signal in the first mode.